Conventional water heater construction includes a generally cylindrical outer shell concentrically placed around the inner water tank leaving an annular space therebetween. The construction is completed by filling this annular space with some type of thermal insulation material, typically liquid, foam-in-place insulation material. The construction is completed by putting some type of top cover or enclosure over the top of the inner water tank and over the upper top edge of the outer shell so as to enclose the annular space. Likewise, some type of lower or base cover or enclosure is provided beneath the water tank in a similar fashion.
The specific arrangement of foam insulation within the annular space may include any of the variations disclosed by the following U.S. patents:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,477,399 Tilton 10/16/1984 4,527,543 Denton 07/09/1985 4,736,509 Nelson 04/12/1988 4,744,488 Nelson 05/17/1988 4,749,532 Pfeffer 06/07/1988 ______________________________________
Tilton discloses a method for insulating a water heater with foamed insulation and includes inflating a tube in the cavity between the shell of the tank in order to define a boundary for the cavity into which the insulating material is injected. The device is then deflated after the foamed insulation has set in the cavity.
Denton discloses a water heater construction with an insulating space between the outer cover member and the inner water tank. A cover is used on the top in order to close off the insulating space and an insulating wall is provided in the insulating space between the tank and the outer cover. The insulating wall is comprised of a plastic envelope member and a wall of insulating material which has been foamed-in-place inside the plastic envelope member.
The '509 Nelson patent discloses a method of making a water heater which includes the steps of locating a sleeve of insulation material around the exterior wall surface of the inner tank extending from approximate the bottom end of the inner tank and extending upwardly longitudinally thereof a predetermined distance which is less than the full length of the inner tank. The next step is folding the top end of the insulation sleeve back over itself in order to form an annular cuff at the top end of the sleeve and the positioning the outer shell concentrically over the inner tank whereupon the annular cuff is compressed between the interior wall surface of the outer shell and the exterior wall surface of the inner tank. The annular clearance space above the annular cuff of the sleeve is then filled with an expandable foam insulation material which is allowed to foam in place.
The '488 Nelson patent discloses a water heater construction where a control apparatus, such as a thermostat, is located on the exterior wall surface of the inner tank and the outer shell includes an aperture which is in alignment with the control apparatus. The specific invention involves the disclosure of a collar which is located around the control apparatus and is compressed between the inner tank and the outer shell in order to provide a sufficiently sealed barrier around the thermostat such that when the space between the inner tank and the outer shell is filled with a foam insulation material, this foam insulation material will not interfere with the thermostat or other control which may be sealed around by this invention.
The Pfeffer patent discloses a water heater construction wherein foam insulation fills a cavity between the tank and the outer shell and is disposed above a bottom wall which is formed by a preassembled fiberglass belt. This fiberglass belt is wrapped and secured around the outer diameter of the tank by an encircling and compressing band. The top and bottom edges of the belt flare outwardly to a diameter size which is in excess of the inner diameter of the shell. A flat, flexible plastic sheet is used much like a shoehorn in order to compress the belt as the outer shell is lowered into position. This flexible plastic sheet is then removed and the space above the belt is foamed with foam-in-place insulation material.
The specific configuration of the foam insulation depends in part on whether the particular water heater is gas or electric. When constructing an electric water heater, the lower portion of the tank does not have special insulation requirements. However, there are operational controls which must be insulated around and a suitable technique for such insulating is disclosed in U.S. Pat. No. 4,744,488 which is expressly incorporated herein by reference.
When constructing a gas water heater, the lower portion of the tank represents a particularly hot area with special insulating requirements. Liquid foam insulation is not suitable for this hot area and fiberglass matting or batt material is used instead. A further feature of typical water heater construction is the need for the water inlet and outlet fittings (pipes) to exit from the tank through the top cover portion of the outer enclosure which is either attached to or fabricated as part of the outer generally cylindrical shell. When a gas water heater is constructed, a flue for the byproducts of the combustion must be provided out the top of the shell in addition to the inlet and outlet water conduits. These conduits and the exhaust flue must be sealed around at the interface with the enclosure or top cover so that as the liquid, foam-in-place insulation rises and expands, it does not leak out around the conduits and flue. In the typical construction approach, a top cover and a bottom cover are assembled to the shell in order to form an enclosed, exterior cylinder.
A variety of insulation materials and insulating methods are used in typical water heater construction in an attempt to produce an energy-efficient unit at the lowest possible cost based on materials and manufacturing labor. This desire has led to the development of many methods for insulating water heaters with a liquid, foam-in-place insulation material such as urethane or polyisocyanurate insulation material. All of the methods currently being used entail the use of sealing devices of some type in order to keep the foam insulation within the space between the tank and the outer cylindrical shell. This approach can be costly in terms of material and labor and other manufacturing concessions may need to be made, such as assembly line speed, in order to accommodate the placement of the sealing devices within the cavity formed by the tank and shell.
Gas-fired water heaters and electric powered water heaters have different design features and thus the sealing considerations prior to foaming are different for each. However, in most conventional manufacturing methods, there are similar constraints for effectively sealing the cavity between the tank and shell. In all commonly used methods, there are several drawbacks that greatly increase the cost of achieving a given energy rating for the water heater. These methods are also a less-efficient use of the costly foam insulation.
The present invention addresses basic principles of the thermodynamics and the processing characteristics of foam insulation in order to provide a more efficient water heater. The present governmental standards requiring higher-efficiency water heaters makes this invention particularly important. Further, the use of fluorocarbons as the most efficient blowing agent in the foaming process allows foam insulations to achieve R values in excess of other commonly used insulation materials. However, new governmental standards aimed at protecting the environment, in particular the earth's ozone layer, are mandating sharper cuts in the use of fluorocarbons. Although it seen that the desire to achieve higher efficiency ratings in terms of R value is in conflict with the government's desire to protect the ozone layer, these competing concerns make the present invention even more important because less foam insulation is required to achieve the same insulation R values and thus as a net result, less fluorocarbons are required in the manufacturing process.
The present invention is directed to the construction of a water heater which is manufactured by first positioning individual sealing gaskets over each protrusion such as plumbing fittings, which extend from the tank, or by first positioning a unitary sealing device over the collective protrusions and then fitting the tank with a top cover which is one portion of the enclosing means for the tank. This top cover has openings to allow the tank protrusions to extend therethrough. This top cover is further configured in such a way as to contact each individual sealing gasket or the unitary sealing device in order to provide a liquid-tight seal at the interface between the operating connections extending from the tank through the top cover with the top cover.
In one approach the next step is to turn or invert the tank and cover assembly so that it is upside down from its normal position so that the top cover is in the lowermost position and the bottom of the tank has assumed the normal top position. The surrounding generally cylindrical outer shell is then positioned over the tank with a concentric space left between the outer surface of the inner tank and the inner surface of the outer shell. Some type of sealing is provided between the shell and the top cover either in individual form or as part of the unitary seal used around the tank protrusions.
As an alternative approach to these first steps, the cover and the generally cylindrical outer shell are preassembled and sealed together in order to create a single unit. This assembled single unit of cover and outer shell is placed over the tank prior to inverting the tank. When the inverting step is performed it is performed for both the tank and the cover/shell assembly.
A further alternative is to fabricate the cover and the outer shell as an integral, one-piece member, such as a molded plastic unit and then assemble this unit over the tank prior to inverting the tank. This eliminates the step of sealing together the cover and shell.
In each of the approaches and alternative forms, expandable insulation foam (liquid, foam-in-place insulation) is injected into the the clearance space between the tank and the top cover and between the tank and the surrounding outer shell. As this liquid foam expands to fill the space, it rises in effect from the top of the tank toward the bottom of the tank. Since the bottom at this point is open, any space or voids left that are not fully foamed are filled with dry insulation such as fiberglass matting or batts which can be easily stuffed into any space left at what will ultimately be the bottom of the foam insulation. Finally, an insulation disc or bottom cover can be placed over the bottom of the tank in order to complete the assembly. After the foam has cured to a sufficient degree, the entire assembly is then inverted back to its normal upright position and the construction is completed.
The value of the present invention evolves from some of the physical and chemical reaction properties of the liquid, foam-in-place insulation. When this insulation material is injected to the annular clearance space between the outer shell and the water tank, when these are in their normal upright orientation, the foaming process begins at a lower portion of the tank along the side of the tank. As the foam rises toward the top of this annular clearance space, the quality of the foam decreases. The lowermost portion of the cavity which is foamed first will have a higher-density foam, and a more uniform density and a more-consistent cell structure to the foam than the uppermost portion of the cavity. This particular result is contrary to the general thermodynamic theory and the heat transfer realities as to heat losses from the inner water tank. Heat transfer and thermodynamics tell us that it is preferred to have the top of the unit better insulated than the lower side portion in order to achieve the most energy-efficient design based upon using a fixed or given volume of foam.
To further compound the manufacturing problems of current foaming methods, a predetermined amount of liquid is injected into the annular space between the shell and the tank and the manufacturing methods rely on the accuracy and consistency of the foam machinery in order to inject exactly the same amount of foam with each unit being constructed. However, there are variations in the cavity volume and variations in how accurately the amount of liquid foam can be controlled as well as simply variations in the foaming process due to the chemistry of the insulation material. The result, as is believed to be well known, is noticeable variations from one water heater to another thus meaning that there is no guarantee that for any one water heater, the annular clearance space including the space between the outer enclosure and the top of the water tank is completely filled with foam insulation. It is known that when under-foamed, the most critical top portion of the tank has insulation voids or openings resulting in a very inefficient design. If too much liquid is injected or if the foam chemistry or temperature vary in such a way to allow a a greater degree of foaming than what has been calculated for the available space, the foam leaks out around the plumbing fittings and other protrusions at the top of the cover and this results in a significant cleanup and appearance problem.
The necessity of high-speed assembly line production simply cannot adequately deal with these variables, and since the over-fill problem cannot be overlooked due to the unsightly appearance, the tendency is to under-design the amount of liquid foam so that any over fill is eliminated. The problem as referenced above is that the top portion of the clearance space, that portion above the water tank top, is very inefficiently insulated and thus the thermal insulation efficiency of the overall construction is inferior.
As mentioned, the present invention solves this problem by providing a more cost-effective and more energy efficient unit by guaranteeing that the top of the unit will always be insulated fully by foam and that this portion of the foam will be of a higher quality. With regard to the amount of liquid foam which is used, there is much greater latitude in view of the fact that any under-fill which leaves a small portion of the annular clearance space uninsulated can be filled with dry insulation material such as fiberglass batting. Since in the present invention the entire outer shell and tank is inverted, the portion that does not receive any foam insulation and is filled with dry insulation material ultimately becomes the bottom or lower portion of the water and is much less critical from a thermal insulation standpoint.